The ultimate goal of this project is to elucidate the structural and functional bases for gustation. The hypothesis that we are interested in is as follows: Morphological differences between taste cells can be correlated with: 1) Properties inherent in taste cells associated with a specific taste field and not the nerve that innervates the taste cells, 2) The physiological properties of the taste cell, and 3) The developmental stage of the taste cell. Our proposed experiments are as follows: 1. Taste buds on the anterior part of the tongue (fungiform papillae) are significantly different from taste buds on the rear of the tongue (circumvallate papillae) with respect to taste bud and taste cell ultrastructure, gap junctions, synaptic structure, and patterns of synaptic connectivity. The results we have already strongly suggest that fungiform taste buds are considerably different from vallate taste buds in the mouse in terms of general ultrastructure and synaptic structure. We will use high voltage electron microscopy, coupled with electron microscopic immunocytochemistry, freeze fracture and computer-assisted three- dimensional (3-D) reconstructions to compare taste cells, nerve fibers, synapses, gap junctions, patterns of synaptic connectivity and the immunoreactivity of fungiform and circumvallate taste buds in the mouse. 2. The distinctive ultrastructural features of taste cell synapses are an inherent property of the receptor cells and not the postsynaptic sensory nerve fibers. Our preliminary data suggest that fungiform synapses are rarer but much more elaborate than circumvallate synapses. One major difference between these two taste fields is innervation. Fungiform taste buds are innervated by the glossopharyngeal (IX) nerve. We will carry out a cross-reinnervation study on fungiform and circumvallate papillae of rodents to learn whether the taste cell or the postsynaptic nerve fiber determines the distinctive features of taste buds. 3. The ultrastructural features of a taste cell can be correlated with its electrophysiological responses. The goal of this experiment is to carry out a structure/function correlation with taste cells isolated from taste buds of the mudpuppy, Necturus maculosus. The mudpuppy was selected for this study because it is polyploid, and its taste cells are much larger, and hence more accessible than taste cells of mammals. Moreover, there is already a wealth of data on mudpuppy taste buds using patch clamp recording technique. We will characterize the ultrastructural features of isolated mudpuppy taste cells that Dr. S. Kinnamon has studied using the giga-seal, whole-cell recording technique. We predict that different cell types will respond preferentially to particular stimuli.